title: Cellular basis of growth suppression by submergence in azuki bean epicotyls.
abstract: OBJECTIVE
  Complete submergence severely reduces growth rate and productivity of terrestrial plants, but much remains to be elucidated regarding the mechanisms involved. The aim of this study was to clarify the cellular basis of growth suppression by submergence in stems.
  
  
  METHODS
  The effects of submergence on the viscoelastic extensibility of the cell wall and the cellular osmotic concentration were studied in azuki bean epicotyls. Modifications by submergence to chemical properties of the cell wall; levels of osmotic solutes and their translocation from the seed to epicotyls; and apoplastic pH and levels of ATP and ethanol were also examined. These cellular events underwater were compared in etiolated and in light-grown seedlings.
  
  
  RESULTS
  Under submergence, the osmotic concentration of the cell sap was substantially decreased via decreased concentrations of organic compounds including sugars and amino acids. In contrast, the viscoelastic extensibility of the cell wall was kept high. Submergence also decreased ATP and increased the pH of the apoplastic solution. Alcoholic fermentation was stimulated underwater, but the resulting accumulated ethanol was not directly involved in growth suppression. Light partially relieved the inhibitory effects of submergence on growth, osmoregulation and sugar translocation.
  
  
  CONCLUSIONS
  A decrease in the levels of osmotic solutes is a main cause of underwater growth suppression in azuki bean epicotyls. This may be brought about by suppression of solute uptake via breakdown of the H(+) gradient across the plasma membrane due to a decrease in ATP. The involvement of cell wall properties in underwater growth suppression remains to be fully elucidated.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ooume
authors.forename: Yuki
authors.initials: Y
authors.lastname: Inoue
authors.forename: Kouichi
authors.initials: K
authors.lastname: Soga
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Wakabayashi
authors.forename: Shuhei
authors.initials: S
authors.lastname: Fujii
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Yamamoto
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hoson
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism / Q000528:radiation effects; D004548:Elasticity / Q000528:radiation effects; D000431:Ethanol / Q000378:metabolism; D007887:Fabaceae / Q000166:cytology* / Q000254:growth & development* / Q000528:radiation effects; D055868:Floods; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D008027:Light; D009995:Osmosis / Q000528:radiation effects; D036226:Seedlings / Q000166:cytology* / Q000254:growth & development* / Q000528:radiation effects; D014882:Water-Electrolyte Balance / Q000528:radiation effects
chemical_list: D000431:Ethanol; D000255:Adenosine Triphosphate